The present invention relates to multicomponent fiber and more particularly to multicomponent fibers having partially overlapping polymeric segments yet are mechanically dissociable or splittable.
Multicomponent segmented fibers include at least two different polymeric components in a single fiber structure. An exemplary multicomponent segmented fiber can include alternating nylon and polyester polymer components. Multicomponent fibers (also referred to as composite fibers) can be split into their respective polymer components to form fine denier fibers, commonly referred to as microfilaments.
For example, multicomponent fibers can be split by mechanical action, such as by drawing the fibers on godet rolls, needle punching, hydroentangling, and the like. Segmented fibers split by mechanical action typically employ polymer segments forming interfaces perpendicular to the periphery of the fiber. It has heretofore been understood that such perpendicular boundaries between adjacent segments promotes fiber cleavage, i.e. prevents occlusion, by eliminating any mechanical interlocking during splitting. Further, to mechanically split the different polymer components, the polymers must be sufficiently incompatible so that the bond between the components can be broken upon mechanical action. However, polymer incompatibility should not be so great that the fiber prematurely splits, such as during the carding process.
Multicomponent fibers can also include a soluble polymer component, which can be dissolved to leave the desired microfilaments. Such multicomponent fibers typically contain polymer segments fully encapsulated in a soluble matrix. However, using a soluble matrix can also be problematic. Manufacturing yields are inherently low because a significant portion of the multicomponent fiber must be destroyed to produce the microfilaments. In addition, waste water or spent organic solvent generated by such processes can pose environmental issues. Further, time required to dissolve the matrix component out of the composite fiber can increase manufacturing inefficiencies.
To overcome these difficulties, mechanically splittable filaments have been developed which include a core polymer segment completely encapsulated by a sheath polymer. Such fibers typically do not prematurely split. However, these fibers require the use of specialized polymer systems to successfully unwrap the sheath in order to achieve the desired degree of splitting. Typically polymers suitable for use in fully wrapped fibers are brittle, and can be expensive, unsuitable for certain end-uses, difficult to extrude, or unavailable commercially.
The present invention provides uniquely shaped multicomponent fibers formed of at least two substantially insoluble polymer compositions arranged as at least three discrete polymeric segments or components. The polymeric segments or components are arranged relative to one another so that at least one segment partially overlaps or occludes at least one adjacent polymeric segment of a different polymer compositions. The partial overlap is positioned at the surface of the fiber so that both the xe2x80x9coverlappingxe2x80x9d segment and the xe2x80x9coverlappedxe2x80x9d segment have at least a portion thereof exposed at the fiber surface, i.e., the overlapping polymeric segment does not completely encapsulate the overlapped polymer segment.
Contrary to conventional thinking in the fiber industry, the inventors have found that the fibers of the invention can be readily dissociated by mechanical action, such as hydroentangling processes, despite the partial occlusion of at least one segment. In contrast to the present invention, traditional splittable multicomponent fibers include polymer segments that are non-occluded, i.e., have polymeric segments arranged relative to one another so as to form distinct unocclusive cross-sectional segments along the length of the fiber so that none of the components are physically impeded from being separated. This was believed necessary to allow the segments to readily dissociate and form microfibers. However, many useful combination of polymers, such as polyester/nylon bicomponent fibers, can prematurely split during carding operations, resulting in loss of product, production problems, lack of cardability, and the like.
One advantage of the fibers of the invention is that the fibers can withstand mechanical action subjected to fibers in many conventional processing operations, such as carding, so that the fibers remain substantially intact until directed to additional downstream processing. This can provide economies of manufacture, minimize lost product, and maintain the ability to card the fibers. The fibers can also remain intact during other fiber processing operations such as drawing, crimping, cutting and the like. However, upon application of sufficient mechanical action to the fibers, for example during a hydroentanglement process, the fibers can then readily split.
In addition the fibers of the invention are mechanically splittable. This eliminates the need to dissolve a polymeric matrix to form microfilaments, and the problems associated with such processes such as solvent disposal, manufacturing inefficiencies and the like.
The mechanically splittable multicomponent fibers of the invention can have a variety of configurations, so long as the fibers include at least one polymeric segment partially overlapping one or more adjacent polymeric segments at the surface of the fiber. Exemplary fiber cross-sectional configurations include without limitation round, oval, rectangular, and the like. Particularly advantageous fiber constructions include round fibers in which the overlapped polymeric segments have a substantially petal or leaf shaped cross-section; round fibers in the overlapping polymer segment is a matrix in which the overlapped segments are partially encapsulated; and oval or rectangular fibers in which the overlapped polymer segments have a substantially rectangular cross section.
The respective polymeric segments of the fibers can be formed of any of the types of polymers known in the art which are substantially insoluble and which can be extruded and fiberized to form fibers. This provides another advantage because conventional polymer systems that are known in the art and are readily commercially available can be used. In contrast, fibers having fully wrapped or encapsulated segments require the use of soluble polymer systems and/or exotic polymers that are not readily available commercially and may have undesirable properties (such as brittleness).
Exemplary polymers include polyolefins such as polypropylene and polyethylene, polyamides such as nylon, polyesters such as polyethylene terephthalate, elastomers, and copolymers, terpolymers and blends thereof. Preferred combinations of polymers for use in the fibers of the invention include polyester and polypropylene, polyester and polyethylene, nylon and polypropylene, nylon and polyethylene, and nylon and polyester. Thus a variety of polymer combinations are available for use in this invention without the concerns associated with conventional bicomponent fiber constructions for the same combination of polymers, such as premature splitting.
The multicomponent fibers can be mechanically treated, for example by hydroentanglement or needlepunching, to effect dissociation of the polymeric components to form a plurality of uniquely shaped microfilaments. The resultant microfilaments take on the shape of the precursor polymeric segments.
Other aspects of the invention include fabrics formed of the mechanically divisible multicomponent fibers which include partially overlapping polymer segments, fabrics in which the fibers have been dissociated so as to provide a plurality of uniquely shaped microfilaments, and methods by which to produce such fabrics. In these aspects of the invention, the multicomponent fibers can be divided into microfilaments either prior to, during, or following fabric formation. Fabrics of the present invention may generally be formed by weaving, knitting, or nonwoven processes. Advantageously the fabric is a dry-laid nonwoven fabric, preferably bonded by hydroentangling.
Further understanding of the processes and systems of the invention will be understood with reference to the brief description of the drawings and detailed description which follows herein.